In many consumer markets, soft touch surfaces are desirable on parts that are frequently touched. In targeted applications, molded parts must also demonstrate appropriate strength, stiffness, and durability required for the application. Articles fabricated from this invention may include automotive interior trim parts such as door panels, consoles, instrument panels, seat closures, and knee bolsters. Non-automotive parts may include chair arms, seat backs, table edges, grips, handles, and other articles that are frequently touched or desired to have a soft or warm touch.
When an object is touched, sensory information is gathered by the skin, joints, tendons and muscles and conveyed to the brain by the nervous system. Tactile feedback is very complex due to the large amount of simultaneously gathered stimuli, which may also include an emotive response associated with a particular surface. Therefore, it is not surprising that whether a user will find a specific surface “pleasant” is difficult to predict.
One example of the benefits of soft touch haptics is evident in soft interior trim versus traditional rigid materials. In the auto industry, leather interior trim has traditionally been limited to use in high end vehicles. Because of the association of leather and luxury, it is not surprising that the use of materials with similar soft touch feel results in an increase in perceived quality, luxury, and comfort compared to hard plastic. Despite having no relevance to the performance of the vehicle, haptic feedback gathered by touching the trim is often influential in the decision of whether or not to purchase a vehicle.
As a result of the increase in perceived quality of soft interior trim, substantial effort and resources have been channeled into creating synthetic materials and resins with touch surfaces haptics.
It is necessary to develop polymeric resins with an improved surface feel as determined by the end user. Additionally, such resins must be formed by processes that are economical and relatively easy to implement.
Hand or machine wrapped “imitation-leathers” have been created from materials including polyurethanes, polyvinyl chloride, and TPOs to try and capture the quality benefit of soft touch without the expense of leather. The soft skin materials are produced by sheet extrusion or casting films and are subsequently wrapped onto rigid substrates. The resulting films have a desirable feel; however, high scrap rates and labor costs make these materials cost prohibitive.
Another method for producing parts with soft touch haptics is to add a functional coating or over molded material layer onto a thermoformed part. Soft touch paints and topcoats, such as those described in U.S. Pat. No. 6,300,419 and U.S. Pat. No. 6,498,214 can be applied to a thermoformed part to increase surface durability and create the desired feel for thermoformed parts. Over molding soft thermoformed skins to pre-formed rigid substrates is also an option, as described in U.S. Pat. No. 7,219,922 and U.S. Pat. No. 6,136,415. Unfortunately, these processes have high scrap rates and manufacturing costs resulting from expensive tooling modifications or multiple post-molding steps.
An object of the present invention is to prepare a blended thermoplastic material that when molded, produces parts with a desirable balance of softness and stiffness, a durable, aesthetically pleasing surface, and a pleasant soft touch feel with reduced scrap rates and manufacturing costs.